The Bible refers to people speaking in tongues--most notably at Pentecost. Is this something that legitimately happens today?
I've been in church services where speaking in tongues has happened, but ...

Was that Pentecost, during which the Holy Spirit was poured out on the apostles in the book of Acts was also a time of jubilee? From what I see, the Pentecost was a holiday to commemorate God's giving ...

I have heard that some Christians consider it the only sure sign of having received the Holy Spirit, which would seem quite important.
If not generally, which groups hold to this belief, and in what ...